A protein termed T (tumor) antigen appears in the nuclei of cells which have been either lytically infected or transformed by tumor viruses such as SV40 and polyoma virus. We have recently shown that SV40 T antigen is a DNA binding protein which has high affinity for SV40 superhelical double stranded DNA. We have developed a millipore DNA binding assay for T antigen, and we propose to purify T antigen, to characterize the purified protein and hopefully to study its function. We plan to work first with normal T antigen from SV40 and with T antigens from temperature sensitive SV40 transformed cells such as the ts, a mutant which does not form T antigen at the non-permissive temperature. BIBLIOGRAPHIC REFERENCES: Stillman, T., Spomer, W.E., and Hager, L.P. Affinity of SV40 Tumor Antigen for Various DNA Molecules. Cold Spring Harbor Abstracts (1975). Jone, C., and Hager, L.P., Iodination of Zeta Protein by Lactoperoxidase, Chloroperoxidase and Chloramine T. BBRC 68, 16-20 (1976).